Hi Jan,

the maximum wiper current ratings of carbon trimmers and cermet trimmers should not be all too different. And I have some datasheets even telling that the maximum current rating is idential. Look here, for instance:

http://www.farnell.com/datasheets/28719.pdf

On the other hand, the minimum wiper current demands of a carbon trimmer is probably higher because of the worse contact situation on a carbon film.

In the past I often had wiper contact problems in audio applications when the audio signal wiper current was too little. In those cases carbon potentiometers were used because of cost reasons. Consequently decreasing the load impedance at the wiper and by this increasing the wiper signal current solved these problems. On the other hand, exceeding the maximum wiper current rating in an OPamp driven circuit is hardly possibly, provided a proper circuit is used.

Another important fact in audio applications is, that no DC current must flow across the wiper, because this would tremendously increase the noise and would render wiper setting changes audible. Even the input bias current of a bipolar OPamp could be too high. So, the consequent use of DC blocking caps arround a pot or trimmer is necessary.

Kai Klaas